iPad cannot be charged or connect with iTunes when plugged in Mac mini or Macbook Pro

Dears,

iPad 1st Gen 3G version

MacbookPro4,1

Macmini5,3

iTunes

the Apple Dock Connector to USB Cable is my common connector for my iPhone and iPad.

the cable works fine with my iPhone 3GS which can sync with my iTunes and charge itself.

the day before still can sync with the iTunes and charge battery.

but today, iPad does not show any sign that it is connected when i have connected the cable.

i have tried with different brand new cable, iPhone works, but iPad does not work.

i have tried with all USB port on Mac mini and Macbook Pro, still no response.

it can be charged via Apple USB Power Adapter.

does anyone have the similar problem?

does anyone can help here?

thank you very much.

regards,

Frank